Internet-based instant messaging applications for exchanging information within selected user groups without the time delays known from conventional e-mail applications are enjoying growing popularity. Typical instant messaging applications allow a user to prepare a message to members of a selected user group, also referred to as a “buddy list”, and to send the message for essentially immediate receipt. In the opposite direction the user similarly receives messages from members of the selected user group.
It is known from 02/43351 that in a communication system a first server is provided for provision of program applications and for data exchange with a first client and a second server for receiving and administering the presence information which is allocated to the first client. Presence information indicates whether a user is currently accessible at a specific terminal in the communication system. The first server is also provided for exchange of data with a second client based on the presence information allocated to the first client.
In the communication system described in 02/43351, the presence information can additionally be combined with a program application. If a user accesses a program application via a terminal for example, the program application allocates the presence information “active” to the user and monitors activities of the user at the terminal. If no user activities are able to be detected for a specific period, the program application causes a check message to be transferred to the terminal. If the user acknowledged the check message at the terminal, the presence information “active” continues to be allocated to the user. Otherwise the user is allocated the presence information “inactive” or a corresponding suitable value. The presence information allocated to the user can also affect the delivery of messages to other users. Such a message is only delivered for example if the presence information “active” is actually allocated to the user. Otherwise the message is deleted or is forwarded to another destination indicated by the presence information.
Instant messaging systems basically require a potential addressee of a message to be accessible. Unlike e-mail systems in which delays in message transmission and in response to messages are the norm, with instant messaging systems sending a message to a first addressee who does not receive the message until hours or days later is generally undesirable. This is why precautions for determining precise presence information allocated to users in a communication system become highly significant.
For convenient administration of “buddy lists” the members of a selected user group can be subdivided into groups in order to improve clarity. A further convenience feature is blocking lists which make it possible for a user to prevent other predefinable users from seeing presence information allocated to him. Alternatively it is possible for these predefinable users to be signaled the presence information “absent” for example, to indicate that the user is not available for the predefinable further users.